The invention relates to the reception of signals which are transmitted in accordance with different standards. For example, television (TV) signals are transmitted in accordance with different standards depending on the country or region and/or depending on the type of transmission which may be analog or digital, via cable, satellite or a terrestrial path.
EP-A 0,696,854 describes a prior-art multi-standard TV receiver. In this receiver, a tuner output signal passes through a surface-acoustic wave filter with a center frequency of 140 MHz which suppresses a great many of adjacent channel signal components. A subsequent mixer stage realizes a frequency transposition so as to obtain a down-converted intermediate-frequency signal of about 75 MHz. The down-converted intermediate-frequency signal is applied to an automatic gain-control amplifier having an internal bandpass limitation, before the down-converted intermediate-frequency signal is applied to the input of an A/D converter. A subsequent band-pass filter having an adaptively controlled bandwidth selects the desired signal with a minimal remainder of the adjacent channel signal components.
It is an object of the invention to provide multi-standard reception which, with respect to the background art receiver, allows more cost-efficient implementations. claims 1 and 5 define a receiver and an integrated receiver-circuit, respectively, in accordance with the invention. Additional features, which may be optionally used to implement the invention to advantage, are defined in the dependent claims.
The invention takes the following aspects into consideration. In a multi-standard receiver, it is possible to convert reception signals transmitted in accordance with different standards to a common intermediate frequency for further processing. The prior-art receiver described hereinbefore as background art is an example of this approach. It requires a tuner, or a group of tuners, which correctly processes the reception signals transmitted in accordance with different standards and converts them to the common intermediate frequency.
In the prior-art receiver, the common intermediate frequency does not correspond to any intermediate frequency which is typically used for a particular transmission standard or a group of transmission standards. Consequently, the tuner which forms part of the prior-art receiver is not suited for applications other than multi-standard reception. Since multi-standard receivers are produced in relatively small numbers, the tuner will be relatively expensive due to lack of economy of scale.
But even if, in the prior-art receiver, the common intermediate frequency corresponded to a typically used intermediate frequency, the tuner would still be relatively expensive due to lack of economy of scale. The tuner would include a substantial amount of circuitry to allow multi-standard reception, which would make it too expensive for applications other than multi-standard reception in which such circuitry is redundant. In a single-standard receiver, one will rather use a relatively inexpensive standard-specific tuner for converting reception signals to the intermediate frequency typically used for the transmission standard in question.
In accordance with the invention, an adjustable frequency converter converts an intermediate-frequency signal provided by a tuner into an input signal for a filter arrangement which is capable of providing various frequency responses associated with different transmission standards. The adjustable frequency converter effectively shifts the intermediate-frequency signal in frequency by an amount which is adjustable to obtain the input signal for the filter arrangement. For any one of a large number of different intermediate frequencies, the adjustable frequency converter can be adjusted in such a way that the filter arrangement receives the input signal in a frequency range which is suitably located with respect to the frequency responses it provides. Consequently, in a multi-standard application, an assembly of standard-specific tuners may be used, each of which converts a reception signal to a different intermediate frequency which is typically used for a particular transmission standard or a group of transmission standards. In many applications, such an assembly of standard-specific tuners will be cheaper, for reasons of economy of scale, than a dedicated multi-standard tuner which is required in the background art. Thus, the invention allows more cost-efficient implementations.
The invention may wholly or partially be implemented as an integrated circuit. For example, the adjustable frequency converter and the filter arrangement may form part of an integrated receiver-circuit for processing intermediate-frequency signals provided by a tuner. Such an integrated-receiver circuit is suitable for relatively many different transmission standards. Consequently, it can be used not only in multi-standard receivers, but also in relatively many different single-standard receivers. Thus, the invention allows an integrated receiver-circuit which is versatile and, therefore, will find a wide range of application such that it can benefit from an economy of scale.